International Journal of Electrical and Computer Engineering (IJECE) Vol. 8, No. 1, February 2018, pp. 43~51 ISSN: 2088-8708, DOI: 10.11591/ijece.v8i1.pp43-51  43 Journal homepage: http://iaescore.com/journals/index.php/IJECE Gauss-Seidel Method based Voltage Security Analysis of Distribution System Gagari Deb 1 , Kabir Chakraborty 2 1 Department of Electrical Engineering, Tripura University (A Central University), India 2 Department of Electrical Engineering, Tripura Institute of Technology, India Article Info ABSTRACT Article history: Received Mar 6, 2017 Revised Jul 27, 2017 Accepted Aug 11, 2017 Complexity of modern power network and Large disturbance results voltage collapse. So, voltage security analysis is important in power system. Indicators are helpful in voltage stability analysis, as they give information about the state of the system. In this paper a new indicator namely Distribution System Stability Indicator (DSSI) has been formulated using the information of Phasor Measurement Unit (PMU).The proposed indicator (DSSI) is tested on standard IEEE 33 bus radial distribution system. The suggested indicator is also applicable to the equivalent two bus system of a multi-bus power system. The proposed indicator is calculated for different contingent conditions at different system load configurations. The result of DSSI is verified with the standard indicator (VSI) which proves applicability of the proposed indicator. The bus voltages of all the buses at base loading and at maximum loading are evaluated for base data and for tripping of most critical line. Keyword: Bus voltages DSSI Load multiplier factor Phasor measurement unit Voltage security Copyright © 2018 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Gagari Deb, Department of Electrical Engineering, Tripura University( A Central University), Suryamaninagar-799022, Tripura, West, India. Email: gagarideb@tripurauniv.in 1. INTRODUCTION Radial Distribution system has a large number of buses. So, it is not possible to maintain adequate bus voltage at each bus. This will increase the chance of voltage instability at the buses [1]. Increase in load demand will reduce the voltage at the receiving end which increases reactive power demand, if the power system is not able to supply the same there will be voltage collapse [2]. For proper operation of power system the voltage stability of the power system should be increased [3]. To improve power system stability and security, planning and operation of power system is essential [4]. Stability analysis may be of two forms- static and dynamic. In static analysis load flow based simulation is performed and in dynamic analysis time domain based analysis is performed [5]. With the implementation of phasor measurement unit (PMU) in power system for voltage security analysis the security level of power system has been increased. Online based methods and offline based methods both have been studied by the researchers for gaining information about voltage stability of power system using phasor measurement unit [6]. Different techniques have been used for voltage stability analysis. P-V curve and Q-V curve method [7-9] are the traditional methods of voltage stability analysis. Many indices such as SVSI [10], L-index [11], L mn and VCPI [12], integrated voltage stability indicators [13] etc. can predict voltage instability in a power system. Other methods such as radial basis function and kohonen’s self-organising feature map can also be found in literature for voltage stability analysis [14], [15]. In recent years a lot of work has been done in the area of voltage stability. Voltage stability analysis was done by the researchers using nodal analysis [16], modified differential evolution [17], coupled single port circuit [18], circuit theory